


memento mori

by ShadowOfASoul17



Category: Cardfight!! Vanguard
Genre: Aged-Up Character(s), F/M, Immortality, Kai is kinda OOC but there is a reason, M/M, Multi, What-If, immortal!Kai, no detailed cardfights here, the OCs are meant to provide some background info and aren't that relevant i swear
Language: English
Status: In-Progress
Published: 2019-02-22
Updated: 2019-02-22
Packaged: 2019-11-03 16:17:03
Rating: Teen And Up Audiences
Warnings: Graphic Depictions Of Violence, Major Character Death
Chapters: 1
Words: 4,025
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17881073
Author URL: https://archiveofourown.org/users/ShadowOfASoul17/pseuds/ShadowOfASoul17
Summary: They say to remember that you die eventually. That's what makes humans human: death's shadow. So what exactly is Kai Toshiki then, if he can no longer die? Cursed to eternally guard Aichi's resting place on the moon with little chance of relief, he clings to what is left of his humanity with a fragile thread...





	memento mori

**Author's Note:**

> If Kai hadn't managed to remember Aichi, then how long would the Quatre Knights have to guard Aichi? A year? Two? A decade? And then I went with the Bad End route with Kai losing and becoming the only guardian. This threeshot is published out of order, so the prequel is chapter 2.

_There was a popular urban legend among Vanguard players._

_No one knew its source, but nearly everyone believed it._

_They say if you wish to get stronger in Vanguard, no matter the reason, your wish will be granted if you wish hard enough._

_A night when the moon is full and you are asleep, you will be transported to a palace on the moon in your dreams._

_There, a throne stands with its back to you. It is surrounded by a sphere of translucent black energy. You will be able to barely make out the outline of somebody sitting in it. If you try getting closer to it, you will be stopped by a mysterious male cloaked in black, who will, without a word, challenge you to a Vanguard fight. He will not introduce himself, but you can call him what seems to fit his role--whether it be a guardian of the throne or a lone warrior._

_If you thought the global Vanguard champions were strong, he is much, much stronger than them._

_He plays a Kagero deck. Even with that knowledge, any attempts to counter it will be destroyed._

_In the end, he will utterly crush you. It may take just minutes, but for you, it will feel like an eternity._

_Then what is the point of even fighting him, you ask?_

_It is said that depending on how well you fought, a certain portion of the sphere's energy is transferred to you and your deck. No one knows how the power works, yet it is said your prowess in Vanguard will improve afterwards._

_Yet in every myth there lies a grain of truth._

_So where then, did this urban legend originate?_

* * *

Ryuzaki Rei didn't believe in urban legends.

Scratch that. 

He believed in some urban legends, but the one about getting stronger in Vanguard after a dream-fight on the moon was simply ridiculous. The way to get stronger in Vanguard was through fights and your own imagination, not dreaming about power. Besides, he and his Shadow Paladin deck worked just fine. He took advice on modifying his deck when he needed it, but other than that, he didn't need power. Nor did he want it. 

His best friend, Mikawa Eisuke, thought otherwise. 

Eisuke wasn't bad at Vanguard, but he always wanted to be stronger. He had fought the world champion once when the latter was touring Tokyo incognito and lost, but it had awakened a desire to be the next world champion. Daily, he would challenge everyone around him to fights, and Rei, being the closest to him, would be challenged twice as often. Out of these matches, Eisuke would win about half the time. 

Whenever tournaments occurred, Eisuke would always drag Rei along with him. The closest they ever got to winning was semifinals. Somewhere after losing so many times, Eisuke started to lose hope in his dream.

Then, in the second year of high school, they heard about the urban legend. One of their classmates, Akatsuki Haruto, had heard it from his brother's friend, whose younger sister had just started playing Vanguard after being inspired by her favourite idol group.

The young girl--Yui, Rei thought her name was--constantly lost but never wavered from her desire to grow stronger. Then, one night, on a full moon, Akatsuki said his brother's friend went to say goodnight to his sister and noticed her deck glowing while she slept. The next day, she had started winning much more often. She hadn't switched clans or anything. Her Genesis deck remained the same, with the addition of a few new units, but it was her strategies that had drastically changed. Akatsuki went on to excitedly announce that Yui had gone on to win a regional tournament, but Rei tuned him out.

He snapped back to reality, though, when Eisuke waved a hand in front of his face, his eyes shining. "Rei, do you think the moon palace would let me challenge the throne guardian?"

"Eisuke, it's a baseless rumour. Don't listen to Akatsuki." Rei said shortly.

"Come on, Rei, stop being such a wet blanket. It sounds awesome!"

"Eisuke, you should stop being so gullible."

Rei hadn't meant for his tone to sound sharp, but apparently, it was a little too harsh--hurt flashed through Eisuke's eyes. He turned away with a huff and began talking to Koizumi Seiji, who sat behind him. 

Guilt filled Rei.  _Maybe I was a bit too harsh. But seriously, it's never been proven and sounds like a cheat code anyways. I'll give him time to cool off and apologize tomorrow._

Then he realized that night would be the night of the full moon. 

Rei glanced over to where Eisuke and Koizumi had started a Vanguard fight. _Eisuke...is your desire for power that great?_

* * *

The next morning, Eisuke didn't answer his door immediately like he usually did when Rei rang the doorbell. After a few more attempts, Eisuke's mother opened the door and told him Eisuke had gone to school early. 

Rei frowned. Eisuke never liked getting up earlier than he had to. This held true throughout their entire childhood and even now, in their second year of high school. This was strange. Very strange.

Rei started off in a run towards his school, a sinking feeling making its presence known in his stomach. 

He arrived at the gates after a few minutes, where Koizumi met him in the courtyard. "Ryuzaki, you won't believe it!"

"What, Koizumi?"

"Mikawa's decimating everyone in Vanguard! He even beat captain Tachibana!"

"What?!" Rei beelined towards the school.

Tachibana Kyosuke, a third-year, was the captain of the Vanguard club at their school and had once won second place at the national Vanguard tournament. No one in the club so far had gotten even close to beating him, and now Eisuke had won?! 

"It wasn't a fluke," Koizumi said, easily keeping pace with Rei's quick strides. "We were all watching. I mean, he probably got lucky with that double critical in the end, but he'd backed the captain into a corner after a few turns!"

"Did his deck change?"

"..."

"Koizumi!"

"...Yes. It did."

Rei stopped so suddenly that Koizumi nearly ran into him. "Tell me everything," he demanded. They were a few metres away from the clubroom, but Rei didn't go in. He leaned against the wall, his eyes boring into Koizumi's.

"His Dark Irregulars deck is gone," Koizumi said softly. "The new deck he's using...it's called Link Joker. They're apparently from Star Gate, and they have a terrifying power to 'lock' units."

"Lock?"

"Basically, you can't use the unit during that turn, nor can you use the circle the unit was locked on. Also...Mikawa's personality has changed."

"How?" Rei asked cautiously. 

"He's colder. More power-hungry, in a sense. He didn't openly taunt his opponents, but everyone could tell he was looking down on them. I didn't battle him so I couldn't completely tell, but even his eyes look like they've changed colour. Did he...did he attempt to follow the urban legend that Akatsuki was talking about?"

"I don't know," Rei replied, his unease growing stronger by the second. "Didn't he say that Yui didn't change at all?"

"Besides a few new units to her deck, her clan didn't change. Only her strategies did."

"Whatever. I'm going in. I'm going to snap Eisuke back to reality and punch him for being an idiot if I have to." Rei pushed himself off the wall and headed towards the clubroom door, ignoring Koizumi's panicked cries to wait.

Rei slammed the door open. "Eisuke!"

Everyone near the door turned to stare at Rei, but he ignored them, searching for Eisuke's distinct red hair. Sure enough, he saw Eisuke in the far corner, battling Akatsuki. Rei stormed over but was stopped in his tracks by Tachibana. "Ryuzaki."

"Captain?"

"From your face, Koizumi told you everything." Tachibana shook his head slightly. "Mikawa's current level of ability far surpasses yours. I don't know how he acquired that Link Joker deck, but it's obviously granting him the power he's always wanted."

"Captain, did you hear Akatsuki's urban legend?"

"To be honest, I thought they were baseless rumours as well. But for Mikawa, it appears to have come true." Rei nodded in acknowledgement and began walking past the captain, but Tachibana gripped his shoulder. "As your captain, I'm ordering you to not fight Mikawa today. I want you to observe him and his deck to the best of your abilities. And then...try forming a deck to counter him."

"Understood, captain."

Tachibana let Rei go, and Rei arrived at the table just as Eisuke started his attack. He and Akatsuki were tied at 4 damage each, but judging from the panicked look on Akatsuki's face, he knew what was coming. All of his rearguards had been flipped face-down--locked, Rei assumed, and he couldn't identify any of the units Eisuke was using. They all looked foreign--and horrifying.

"I attack your Vanguard." Eisuke's voice was cold, just as Koizumi had described, and held no mercy. It was completely unlike his normally cheerful tone, and Rei shuddered,

A drop of sweat rolled down Akatsuki's neck as he put down the only card in his hand. "I guard with Guidepost Sage, Elron!" With a shield of 10000 combined with his Vanguard's attack, Eisuke would need a double critical to win. 

"Drive trigger, check." Eisuke flipped over the first card. "First check. Critical trigger. I give all the effects to my Vanguard. Second check...critical trigger. I give all the effects to my Vanguard."

"Damage check!" Akatsuki cried. He flipped over two cards, but he didn't draw any heal triggers. The cards landed in the damage zone, and he fell to his knees in defeat.

"I win," Eisuke said smugly. "This deck is beyond what you guys can beat right now."

"Is it true then? You battled the guardian on the moon?" Akatsuki asked, his voice barely above a whisper as he collected his cards. The Royal Paladin deck he was so proud of had been easily defeated by Eisuke. 

Eisuke's smirk was the only answer. 

Rei had enough of watching his best friend act like a complete stranger. "Eisuke!" He stepped forward and punched him in the chest. "What did you do?!"

Eisuke stumbled back, but he raised his head to gaze at Rei. Rei recoiled when he noticed that Eisuke's light brown eyes now had a ring of black around them. "I got the power I wanted. I can finally become the world champion like this!"

"Do you  _want_  to become world champion like this? Looking down on your opponents and getting rid of your Dark Irregulars deck that you love so much?! What did you do, Eisuke?! Are you even the Eisuke I know?!" Rei grabbed Eisuke's shoulders. "Answer me!"

"Why don't you try for yourself, then?" Eisuke smiled, but there was no emotion in it. "At first I just wanted to prove you wrong and that Akatsuki's urban legend was right, but Rei...don't you want power as well? You'll never defeat me with your Shadow Paladin deck now." Eisuke pried Rei's hands off him and leaned in close to whisper into Rei's ear. "Think about it," he breathed. "The ultimate power that beats everything...don't you want to try it out?"

Rei stood there, frozen, as Eisuke stepped away. "Well, see you around, Rei. I'm going to find some stronger opponents to beat. Tell the teachers that something at home came up, okay?"

"H-hey, wait! Eisuke!" It was too late. Eisuke had disappeared out the door and no one had stopped him. 

Rei turned away with a sigh and saw that Akatsuki was still standing at the table, staring at his deck. "Tell me how the urban legend went again."

Akatsuki's head snapped up. "Don't tell me--"

"I don't want that kind of power. If Eisuke really got that deck after battling someone on the moon, I'm going to challenge him and bring Eisuke back to normal. It's your fault for spreading the legend, but it's also my fault for not noticing how deep his desire for power was despite being his best friend. And as his best friend, I'm bringing him back."

Akatsuki sighed in defeat. "All right."

* * *

_Full moon, check._

_Deck beside me, check._

_As for my desire..._

Rei sighed. He sat on his bed, staring at his deck. If what Akatsuki heard him was true, then only the people with the strongest desire for power were chosen. 

_Is my desire for power to bring Eisuke back to normal stronger than people who just want raw power in general?_

Rei lay down and closed his eyes, desperately wishing with all his might for anything that would bring back the boy he'd known since they were toddlers. He didn't want to see his best friend like this. He wanted the cheerful, snarky, and often-gullible Eisuke back. 

_Please...let me see Eisuke smile like he used to one more time._

As he drifted off to sleep, a single tear rolled down his face.

* * *

Rei opened his eyes to unfamiliar surroundings. He was in a wide open area looking out into a black sky dotted with stars. White columns supported a white roof. The centre appeared to be sunken deeper into the ground, and a white throne stood, a sphere of translucent black pulsing gently around it. He slowly turned around and saw the Earth floating in space. He started in surprise.

_I'm not on Earth? Does that mean...it worked?_

Looking down, Rei found that he was now wearing his school uniform. His deck was in his pocket. Running a hand nervously through his dark blue hair, he walked towards the throne.

A figure in a hooded black cloak coalesced out of the shadows and blocked Rei's path.

Rei shouted in surprise and stumbled back. "Who are you?!"

_He will, without a word, challenge you to a Vanguard fight. He will not introduce himself either._

Akatsuki's words ran through his head, but Rei started when the figure spoke. "You...you are different." The voice was hollow and strained as if the figure hadn't spoken in years. "You crave for power, but you don't want it for yourself."

Rei steeled his nerves. "You're the one who fought my best friend, Mikawa Eisuke, aren't you? Ever since he fought you, he's undergone a complete personality shift and discarded his old deck. What is Link Joker? Why did you choose to fight him? Why did his personality change?"

"I don't pick who comes here. What draws people here is their desire for power. Their reason does not matter."

"Your kind of power corrupts people!"

"Only if they let it corrupt them. Your friend is not a unique case out of the worlds I've been in."

Worlds? "...Are you human?"

The figure tilted his head up slightly so Rei could see his lips turn up in a bitter smile. "A long time ago. Now, if you truly want to save your friend, I will test your resolve."

A floating Vanguard mat appeared before Rei, and he set his deck down.  _If I recall correctly, Akatsuki said he plays a Kagero deck. That's nothing new to me. The captain sometimes uses a Kagero deck and Koizumi does as well._

"Are you ready?" The figure asked emotionlessly.

"Yes. Stand up, Vanguard!"

"Stand up, the Vanguard."

Rei made no comment at the extra word but noted it as something out of the ordinary. "Darkside Trumpeter!"

"Lizard Runner, Undeux."

_Hang in there, Eisuke. I might not defeat this guy but I will bring you back to normal!_

* * *

The final damage card floated into Rei's damage zone, and he collapsed to his knees, breathing heavily. He had been utterly defeated. 

"Your potential surpasses your friend's. If you truly wish to save him, you must defeat him in a Vanguard match. He will return to normal after that."

"How do I defeat him?" Rei asked cautiously.

The figure didn't reply but turned to watch as a bubble of energy rose up from the sphere surrounding the throne, floating over to Rei's deck and surrounding it in black light.

"Hey, what are you doing to my deck?!" Rei tried picking it up but received an unhealthy shock for his troubles. He yelped in pain and cradled his hand close to his chest.

The figure did not reply. The glow eventually died down from Rei's deck and he reached for it again. He was successful this time, and he hurriedly flipped through his cards, making sure they were all there.

"Your clan has not changed. Relax. Link Joker cannot possess those with pure intentions or those who reject its power wholeheartedly." The figure turned away as he spoke, but Rei could hear him mutter two words under his breath. "Unlike me."

"What happened to you?" Rei asked quietly. "I'm not a detective, but there are some pretty glaring clues. There's someone sitting on the throne behind you and surrounded by a barrier. Were they sealed away? You're the only one here and you stop anyone who tries to approach the throne, but if they face you in a Vanguard match, some of the sphere's power is transferred to them. And despite what you say...you are human, aren't you?"

The figure stilled before he threw his head back and laughed. The laughter was full of resentment and pain. "You're smart. But you're wrong on one part: how can I be a human if I can't die?" 

"You can't die?!"

"I've been cursed." The figure spoke simply. "Your friend is lucky to have someone who cares for him that much and is still alive to bring him back to normal. Now go back. I've said too much." He snapped his fingers, and a mass of shadows rose up from the ground, engulfing Rei. 

"Hey! Wait!" Rei struggled to break free from the shadows but stilled as he watched the figure flip back the hood to reveal his face. 

A young man--hell, he looked around Rei's own age, with messy brown hair and a handsome face. But what struck Rei the most were the male's dark green eyes. They were filled with an ageless torment and sorrow. For a moment, he looked much, much older than Rei assumed him to be. As their eyes met, the emotions faded from the male's eyes and dulled to a blank, empty green.

As Rei continued to lock eyes with the male, the emptiness in the latter's eyes seemed to suck Rei into them, but he then realized the shadows were pulling him further and further away from the palace.

"Wait!" Rei screamed...

* * *

...and bolted upright in his bed, sweating profusely. 

Rei blinked. His deck was on the table beside him. The curtains were open, allowing sunlight to stream into the room. Checking the clock, it read 6:00 AM. 

Rei groaned and rubbed his eyes. Was it all a dream?

Grabbing his deck, he flipped through his cards. His eyes widened as he saw some new units.  _These weren't here before! Then last night..._

The high-school student around his age. 

A face tormented with pain and guilt that accumulated over who knows how many years.

Eyes that were empty yet held traces of madness in them.

Shadows engulfing him as he stared into bottomless pools of despair.

__Just who was that person? And why was he cursed?_ _

* * *

Rei arrived at school at the same time as Akatsuki and Koizumi. Akatsuki approached him first. "Did you do it?"

Rei held up his deck. "Try me when we get there."

"You're sounding awfully confident," Koizumi remarked. "Weren't you shell-shocked yesterday?"

"Believe me; I'm trembling really badly right now. But Eisuke takes higher priority."

"Details, Ryuzaki, I want details!" Akatsuki begged. "Did he talk? What was his deck like? What did the throne look like?"

"I don't remember much," Rei lied, reluctant to share details about the guardian's tormented state. "He didn't talk much during the fight except to explain card effects. His Kagero deck is way better than Koizumi's, no offence to you. As for the throne...there was definitely someone inside."

"Like a seal?" Koizumi asked.

"I knew it; then he definitely was a guardian!" Akatsuki said excitedly. "I'm jealous now; you got to see something really cool!"

"Eisuke did as well and look at him," Rei said sadly. 

Akatsuki and Koizumi shut up, guilty looks on their faces. "Sorry, Ryuzaki. I wasn't thinking," Akatsuki apologized.

"It's fine. I'll bring him back to normal and we'll goof around like we always do."

"Yeah!"

* * *

On a screen brought up by his own power, Kai Toshiki watched as the sixth card landed in Mikawa Eisuke's damage zone. The seed in Eisuke's soul split in half and lost the power to control him. One half remained in him, and the other transferred itself to Ryuzaki Rei's soul. The fragments of the seed would continue to split as the boys fought other opponents, and soon, Link Joker would integrate into that universe's planet Cray as a new clan. 

Kai watched as Rei tightly embraced Eisuke with tears running down his face. He could not hear what they were saying, but the joyful expressions on their faces made it clear.

And suddenly, the screen was shattered with a clenched fist. 

"Damn...it's been too long..."

He had long lost the capability to feel emotions such as joy. He only felt bitterness, anger, guilt, and sadness, and even these emotions were slipping away from him, leaving him numb and empty. Soon, he thought with a sardonic smile, he would be reduced to little more than a machine, incapable of feeling anything and monotonously carrying out the tasks that were assigned to him so long ago.

It was strange, how immortality changed people.

How long had it been since he last talked to someone he truly knew?

How long had it been since he last felt the touch of another human being?

How long had it been since he last saw someone smile at him, say his name, talk to him, or even look at him with acceptance in their eyes?

Kai slowly walked over to the barrier that surrounded the throne. It was semitransparent, and he gently rested a hand on the barrier, gazing at the person slumbering on the throne.

How long had it been, since he had last seen those blue eyes open, the bright, honest face smiling at him, calling his name?

_"Kai-kun!"_

"Aichi..." 

Sinking to his knees, his body shook with emotion. He had long since lost the ability to cry, but his grief showed in other ways.

Ryuzaki Rei had been the very first person out of many who challenged him to save another from Link Joker's power. His world had been the first out of many who had a fighter like that. Something about that boy had triggered something in Kai. Something he hadn't felt in a long time. 

Old memories blurred with new. Faces he thought had long faded away resurfaced in his mind. 

Ryuzaki Rei used a Shadow Paladin deck.

_Ren..._

Mikawa Eisuke used a Dark Irregulars deck.

_Tetsu..._

That girl used a Genesis deck.

_Tokura..._

_Everyone..._

With a growl, Kai Toshiki reached out and a shadowy blade formed in his right hand. He swiftly stabbed his left hand, hissing in pain as dark blood began flowing from the broken skin. However, he didn't bleed much as his skin knitted itself back together the moment he yanked out the blade. But he had gotten what he wanted. The brief jolt of pain, a feeling he hadn't experienced in decades ever since he realized attempting to kill himself wouldn't solve anything, cleared his head. 

"I will discard all my emotions and my humanity if I have to," he muttered, rising to his feet and letting the blade dissipate. "Everyone I know is dead. I have not failed in my orders for centuries, and I will not fail now."

He melted into the shadows, an unspoken thought clear. 

_Until Aichi is permanently released from Void's power and free from my mistake, I cannot fail._


End file.
